German Offenlegungsschrift DE-OS 32 35 442 discloses an automatic bobbin winding machine in which yarn cops and empty cop tubes are circulated on individual pallets, sometimes referred to as peg trays. During their presence in processing stations and over major portions of the transport system, the cops and tubes remain on these pallets.
It is known that in preparation for the cop unwinding process in a bobbin winder, cops must be rotated about their longitudinal axis so that the leading end of the yarn can be located and placed in a ready position. To that end, drive wheels are in many cases disposed to frictionally engage with the cop base to transmit the rotary motion directly to the cop. In the apparatus of DE-OS 32 35 442, each pallet is held by retaining elements to prevent its rotary motion. A driven friction wheel pivots against the base of the cop and rotates the cop on the spindle of the pallet. Any yarn windings that may be present at the base of the cop are clamped by the friction wheel and as a result cannot come loose. To prevent the friction wheel from contacting the main yarn package of the cop, the friction wheel must be positionable quite close and very accurately.
In a winder described in German Patent DE 39 25 987, the pallet is driven, with the rotary motion being transmitted to the cop by tilting the cop. Although this technique improves the transmission of the rotary motion, at the same time, it results in increased frictional wear at the tip of the cop.
It is also known, in individual cop processing stations, to engage clamping elements outwardly against the cop base in order to keep the cop firmly held on the spindle of the pallet when upwardly oriented vertical forces are being exerted. Such clamping elements are described in German Patent 34 26 655 for a yarn end preparation device and in German Patent DE 39 08 487 A1 for a winding station. For that purpose, clamping and triggering elements are required at each processing station. In each case, the danger exists that yarn windings may also be clamped, which causes damage to them or can directly cause yarn breakage in the winding position.
In the case of transport paths that proceed over various levels, as described for instance in German Patent DE 40 15 173 A1, the pallets with the cops or tubes are tipped, which creates the danger that the cops or tubes may slide off the spindles of the pallets in response to external factors or from a change of the direction of movement.
German Patent DE 40 16 466 A1 discloses a textile machine which circulates pallets whose spindles have at least one elastic element on its circumference in order to securely hold or carry the textile bobbin or tube. The elastic element has sufficient resiliency to exert a radially outward force relative to the longitudinal axis of the spindle. Although the spindles of the pallets have the advantage over the pallets initially discussed above that the cop is securely fixed on the spindle, i.e., the cop cannot readily be doffed from the pallet and also rotates unitarily with the pallet, these pallets nevertheless share the disadvantage that the various pallets can be used only for a very specific bobbin size with a predetermined inside tube diameter. A further disadvantage is that wide tolerances in a batch of bobbins or deformation of the bobbin tubes result in considerable differences in the tube clamping force achieved.